The Q&A Archives: Insect boring into strawberry crown

Question: My strawberry plants are being damaged by an insect that burrows into the crown, causing the leaves to yellow. The stress eventually kills the plant. What can I do? Beverly Stephens Smyrna, GA

Answer: Your problem could be either white grubs or the strawberry crown borer, says Kenneth Sorensen, an entomologist at North Carolina State University in Raleigh. White grubs are the larval form of the Japanese beetle or May beetle. The adult emerges from the soil in early summer and lays white eggs in the soil. The larvae that hatch three weeks later feed on roots and crowns of a wide variety of plants, including strawberries. In fall they migrate deeper into the soil to overwinter. The larvae feed again all through their second year, then emerge as adults the following spring. For white grub control, the quickest solution is to remove and destroy infected plants and when the soil temperature is above 55_F, apply beneficial nematodes in early evening,watering them in well, says Sorensen. The nematodes won't harm grubs already in the plants, but they will begin killing grubs still in the soil within 10 to 30 days. For long term control of grubs, apply milky spore disease on the lawn and grassy areas around the strawberry patch this August, advises Sorensen. Although the milky spore bacteria infect grubs within a few weeks after application, milky spore generally takes a full season to get established. (See National Gardening, September/October 1992, for more on this biological pest control.) If the grubs are legless, then you're probably dealing with the strawberry crown borer larvae. The dark brown adult beetles emerge from the soil at blossom time to lay eggs on the plant's crown. The resulting white larvae burrow into the crown to feed and grow, killing the plant. If only a few plants are affected, the simplest control is to destroy them, says Sorensen. If you have a severe infestation, you can beat the borer by growing strawberries as an annual planting in October and harvesting in June, he says. Till the infested planting in summer to kill most of the larvae. Two strawberry varieties that have performed very will in this area on an annual cropping system are Chandler and Douglas, Sorensen notes.

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